Technique to get a more organic shape from a base model head
The head is box-modeled from a uv-sphere. The video is a timelapse but you can follow along if you stop it after each step, basically after each second ;-)
Most of the time you only have to move vertices along the axis a bit and add new geometry with the knife tool (K in Edit mode). For the neck (a cylinder) add edge loops with Ctrl+R.

How to Get It In Shape
The mentioned relaxation of the vertices can be achieved in Blender with the Smooth brush, which also works with low-poly mesh. After you added the new edges switch to the Sculpt Mode. Select the brush with a very small strength (~0.08) and touch the top of the head, the forehead, cheeks and chin area.  The Smooth brush reduces the volume and the chin will get smaller if you touch it a few times.
The flat area of the ears can be pulled out slightly if you pull the pole and the vertices around it to the side. Use the Snake Hook brush or Elastic Deform brush. This will give the head a rounder appearance.
Then pull the outer vertex of the cheekbone downwards with the Snake Hook brush (alternatively, you can do this in Edit mode). Finally, move both vertices that form the cheekbone a bit forward, along the y-axis, to give them more volume.
That's it.
Later, when the mesh has a higher density, you can use the Smooth brush to smooth it, the Elastic Deform and the Inflate brushes to restore the volume and to adjust the shape.
The relax tool (in the Loop Tool add-on) is great to smooth edge loops. For example when you messed up the lips or the eyelids.
It is best to see the changes in the frontal view: